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Polygonum americanum (Fisch. & C.A.Mey.) T.M.Schust. & Reveal

Polygonaceae · Missouri, Oklahoma +9

English names not checked: Wikidata's common names were not read for this page.

Photographs not checked iNaturalist and GBIF media were skipped (not asked) when this page was built. Not asked, or not answered, is not "none": nothing here claims there is none. Why the site says it this way.
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Habitat figures
Cold floor (1 night in 100)
-5.7°C
Record low -14.4 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
33°C
Jul at the habitat CHELSA
Rain a year (median across the range)
1,203mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
16–40DLI
Lowest to highest month (DLI) CHELSA
The year in your months, northern hemisphere
  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec
Rain spread: 70% of the median year's rain takes 8 months, so no short rainy season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Polygonum americanum, commonly called southern jointweed or American jointweed, is a species of flowering plant in the knotweed family. It is native to Southeastern United States extending in scattered locations west to New Mexico. Its preferred habitat is dry, sandy areas.

Quoted from Wikipedia, "Polygonum americanum", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (817 mm of 1,161 mm) takes 8 months, December to March and June to September. Mean temperature moves 19.8 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to March and June to September.

Rain

1,161 mm in the median year at the habitat, 817 mm of it December to March and June to September. Wettest month June at 118 mm, driest month April at 82 mm. Across the grid cells of the range the year's total runs 951 mm to 1,398 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 1,203 mm, is the year's rain at the top of the page; the 1,161 mm here is the median year's, the twelve monthly medians added, which the rain rule reads. Habitat calendar, northern hemisphere; median year across the grid cells of the range, CHELSA.

Light

Open sky over the habitat: 16 to 40 mol/m²/day across the year (daily light integral, median year across the grid cells of the range, CHELSA; the lowest 10th-percentile month across the cells is 15, the highest 90th-percentile month 43).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -5.7 °C, the absolute minimum -14.4 °C, 1,617 frost nights in 44 years, 36.8 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 38.5 °C. Monthly means: the coldest month's mean nightly low 3.4 °C in January (across the grid cells of the range -0.6 °C to 6.8 °C), the warmest month's mean daily high 32.5 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: -5.7 °C, which is the 1st-percentile night over 44 years at a typical spot in the range (NASA POWER).

Humidity

Relative humidity at the habitat: 55 to 59% across the year (monthly means, median year across the grid cells of the range, CHELSA). A figure about the air, saying nothing about how the plant takes water.

How this section is made

Each card states this species' habitat figures with their sources, and what two fixed rules read from them; nothing here says what the plant does, wants or tolerates. The rules · the terms.

Seasons. Read from the median year of CHELSA monthly rainfall and mean temperature across the grid cells of the range: the rain rule takes the smallest set of months carrying 70% of the rain and calls it winter when its mean is more than half a degree below the year's, summer when more than that above, and neither in between; the temperature rule, used only under 120 mm, names the cooler six months when they are at least a degree cooler than the other six. Months are shifted for the other hemisphere only where the temperature curve moves 4 °C or more and the habitat lies 10° or more from the equator. A reading of the curves, not an observation of the plant.

Rain. CHELSA monthly precipitation, median year across the grid cells of the range. The rain that falls where the species is recorded; nothing about how the plant takes water.

Light. CHELSA shortwave radiation at each envelope cell, a daily-mean flux taken to a daily total and converted at 2.07 mol of PAR per MJ. The sky over the habitat, measured; what reaches a plant under a rock, a shrub or a shade cloth is not.

Temperature. NASA POWER daily minima and maxima over 44 years at a typical spot in the range, lapse-corrected -12 m to its elevation; CHELSA monthly means, median year across the grid cells of the range. The cold floor is the 1st-percentile night named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity. CHELSA relative humidity, median year across the grid cells of the range.

Climate across the habitat

Habitat months, northern hemisphere

Habitat climate of Polygonum americanum through the yearWarmest month July, mean daily high 33 °C; coldest month January, mean nightly low 3.4 °C; 1,161 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA; the extremes at the edge from NASA POWER. Habitat months, northern hemisphere.-20°-10°0°10°20°30°40°frost38.5° 99th-percentile day, NASA POWER-14.4° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0255075100125150mm rainDLI 16–40RH 55–59%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 150 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low extremes over 44 years at a typical spot in the range, from NASA POWER, marked at the edge, in no month DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C13 / 10–1715 / 12–1920 / 17–2224 / 22–2628 / 26–3031 / 30–3233 / 32–3432 / 31–3429 / 27–3124 / 22–2719 / 15–2214 / 10–17
Night °C3 / -1–75 / 1–88 / 5–1212 / 10–1617 / 15–2021 / 20–2323 / 22–2422 / 21–2419 / 17–2214 / 11–179 / 6–125 / 0–8
Rain mm95 / 65–111101 / 62–120111 / 74–12882 / 64–12387 / 71–150118 / 99–135113 / 61–14089 / 63–13589 / 77–10689 / 78–13786 / 72–127101 / 69–131
DLI18 / 17–1922 / 21–2329 / 28–3037 / 35–3739 / 37–4040 / 39–4240 / 39–4337 / 34–4031 / 30–3325 / 24–2719 / 17–2016 / 15–17
RH %58 / 57–5957 / 56–5956 / 55–5855 / 53–5856 / 55–6159 / 58–6159 / 57–6059 / 56–6158 / 56–6057 / 56–5857 / 56–5958 / 57–59
How this section is made
Each figure is the median across the 150 grid cells holding the 268 in-range records, with the 10th–90th percentile span across those cells after the slash where it differs. A dash is a month one or more of those cells has no figure for in the grid (a variable CHELSA does not carry there), so no median is taken rather than one over fewer cells. Extremes and elevation were read at a typical spot in the range, cell 1129:1960 (33.525, -81.975). Over 44 years there: absolute minimum -14.4 °C, 1st-percentile night -5.7 °C, 99th-percentile day 38.5 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Across the range: median and 10th–90th percentile of each month across the 150 distinct grid cells holding 268 of the 268 in-range records; extremes and elevation at the typical cell 1129:1960 (its coldest month's mean nightly low nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 33.50_-81.875, lapse-corrected -12 m at 6.5 °C/km. Elevation: ETOPO 2022, 100 m (cell mean).

Natural habitat

Native range as published by WCVP; the marker is where the records are densest and decides nothing: the climate was read across the cells of the in-range records placed well enough to read one, not at the marker.
Openly licensed records inside the range, framed on where they fall.

This species has no GBIF key of its own. Its records are GBIF's under the key of the name Kew's World Checklist holds as this plant: 5334502 (Polygonella americana (Fisch. & C.A.Mey.) Small, 649 records). No name was matched to GBIF; the keys are read from Kew's synonymy. How.

NativeMissouri, Oklahoma, New Mexico, Texas, Alabama, Arkansas, Georgia, Louisiana, Mississippi, South Carolina, Tennessee · regions are the level-3 units of the World Geographical Scheme for Recording Plant Distributions, as Kew's World Checklist records ranges, some under historical names such as Yugoslavia or Czechoslovakia (how).
Map marker29.972, -96.502 · in the densest population, 302 records (65% of those in range)
Kew's description“subshrub” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 467 georeferenced records inside the native range; the climate across the range on the 268 of them placed to within 10 km; the map shows only the 197 openly licensed ones, which alone would put the marker 35 km away. 4 records outside the WCVP native range not used. 199 in-range records are placed to worse than 10 km, or with no stated accuracy (admitted only as a person's observation to three decimals), and stay on the map but off the climate.
Other GBIF keysRecords also from GBIF's key 5334502 (Polygonella americana (Fisch. & C.A.Mey.) Small): Kew's file holds it as Polygonella americana (Fisch. & C.A.Mey.) Small (synonym under Polygonum americanum (Fisch. & C.A.Mey.) T.M.Schust. & Reveal); 649 records, from GBIF's download.
How this section is made
The map marker: the openly licensed record nearest the middle of the densest 1° population inside the densest 4° block of the 467 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Not checked. iNaturalist and GBIF media were skipped (not asked) when this page was built. Not a statement that none exist.

Similar habitat climate The 6 nearest by mean daily high, mean nightly low and rain, month by month. How.

Trillium reliquum Trillium reliquum Relict trillium Photo: CC0, author not statedNolina georgiana Nolina georgiana Georgia bear-grass Photo: CC BY, Scott Allen DavisToxicodendron pubescens Toxicodendron pubescens Atlantic poison oak Photo: CC BY, Brandon CorderMacbridea caroliniana Macbridea caroliniana Carolina birds-in-a-nest Photo: CC BY, Alison NorthupClinopodium carolinianum Clinopodium carolinianum Georgia calamint Photo: CC BY, Leila DasherPenstemon australis Penstemon australis Eustis Lake beardtongue Photo: CC BY, Raven Dandridge

Other Polygonum 10 in the reference

Polygonum arenastrum Polygonum arenastrum Equal-leaved Knotgrass Photo: CC BY, Bernhard HildebrandPolygonum aviculare Polygonum aviculare Prostrate knotweed Photo: CC BY, Daughter DadPolygonum douglasii Polygonum douglasii Douglas' knotweed Photo: CC BY, Dan RileyPolygonum equisetiforme Polygonum equisetiforme Horse-tail knotweed Photo: CC BY, Duarte FradePolygonum maritimum Polygonum maritimum Sea Knotgrass Photo: CC BY-SA, Emanuele Santarelli Polygonum nesomii Polygonaceae Polygonum paronychia Polygonum paronychia Beach knotweed Photo: CC BY, Konshau Duman Polygonum polygamum Polygonaceae Polygonum scoparium Polygonum scoparium Polygonaceae Photo: CC BY-SA, Sergio costantini Polygonum smallianum Polygonaceae

Names & registers

Also known as Polygonella meissneriana; Polygonella ericoides; Polygonella americana; Psammogonum americanum; Gonopyrum americanum. (WCVP, RBG Kew)

IPNIPOWOWikidataWFOWikipedia

The record

Family
Polygonaceae
Described by
(Fisch. & C.A.Mey.) T.M.Schust. & Reveal
Native to
Missouri, Oklahoma, New Mexico +8
Wild records
467 in range · 197 open

Every figure here is derived from public data by a stated rule and names its source; nothing about this species is written for its page by a person or by AI, apart from the marked, credited quotations. How →

Where this page came from built 2026-10-22
Kew's names (WCVP) kew.names answeredas of 2026-06-04Kew's entry Polygonum americanum (Fisch. & C.A.Mey.) T.M.Schust. & Reveal (plant_name_id 2914490), read from Kew's names file
GBIF species record gbif.species not askedGBIF's backbone holds no one accepted species of this name, and a name it holds only as another species' synonym is not taken for this one, so GBIF's records were not asked
GBIF synonyms gbif.synonyms not askedGBIF's backbone holds no one accepted species of this name, and a name it holds only as another species' synonym is not taken for this one, so GBIF's records were not asked
GBIF common names gbif.vernacular not askedGBIF's backbone holds no one accepted species of this name, and a name it holds only as another species' synonym is not taken for this one, so GBIF's records were not asked
WCVP native range wcvp.distribution answeredas of 2026-06-04
GBIF occurrence records gbif.occurrences answeredas of 2026-10-21this species has no GBIF key of its own; its records are read under GBIF's keys for the names Kew's file holds as this plant, never by a name matched; GBIF occurrence download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 649 records of GBIF's key 5334502, Polygonella americana (Fisch. & C.A.Mey.) Small (Kew's file holds it as Polygonella americana (Fisch. & C.A.Mey.) Small (synonym under Polygonum americanum (Fisch. & C.A.Mey.) T.M.Schust. & Reveal)): the GBIF download; 1 record within 1 km of a botanic garden, herbarium or zoo left out (1 at a botanic garden or arboretum; Wikidata's list)
Habitat climate climate answeredasked 2026-10-22
Daily extremes (NASA POWER) climate.extremes answeredasked 2026-10-22NASA POWER (MERRA-2) daily 1981–2024, cell 33.50_-81.875, lapse-corrected -12 m at 6.5 °C/km
Wikidata wikidata answeredasked 2026-10-22found by Kew's IPNI identifier 77117330-1, POWO 77117330-1
Wikipedia wikipedia answeredasked 2026-10-22
iNaturalist taxon inat.taxon not asked
iNaturalist photographs, wild inat.photos.wild not asked
iNaturalist photographs, cultivated inat.photos.cultivated not asked
GBIF media gbif.media not askedGBIF's backbone holds no one accepted species of this name, and a name it holds only as another species' synonym is not taken for this one, so GBIF's records were not asked
Wikimedia Commons commons nothing to reportasked 2026-10-22
OpenAlex papers openalex not askednot yet asked for this reference; a later fill takes the papers from OpenAlex's snapshot

Every source is recorded as having answered, reported nothing, refused, failed, not been asked, or answered twice where one answer is taken (“not taken: two items answered”), and, for a source asked when this page was built, when: the figures are as the source held them that day; a source read from a file (Kew's World Checklist, a GBIF download) says "as of" the file's day instead; a row carried from an earlier build of the page names that build instead. Only “nothing to report” is ever shown as an absence. Records came from 45 datasets via GBIF.org; each carries its own licence.

Cultifolio

Opening your plants…